Integrated modelling of climate and land use change impacts on groundwater flooding risk in a Chalk catchment
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From 2010 The Flood and Water Management Act has given the Environment Agency and local authorities in the United Kingdom a statutory requirement to manage flooding from groundwater. A robust, long-term groundwater flood risk assessment methodology was developed using the Pang/Lambourn catchment in West Berkshire as a case study. A recharge model based on a soil moisture budget was built in GIS and tested against observations. The timing and mechanism of flow in the vadose zone was also assessed using cross-correlation analysis between rainfall and borehole responses for a better understanding of recharge processes. Regional MODFLOW models were developed for saturated groundwater flow using input from the recharge model. This integrated model was then coupled with a Global Climate Model using a stochastic weather generator to downscale output to the catchment. An ensemble of high and low climate change scenarios suggests there will be between a 5.5% and 27% reduction in recharge over the coming century and mean groundwater levels will lower by up to 3.8%. Land use modification characterised by afforestation and urbanisation resulted in nuanced changes in the spatial distribution of recharge as well as a further mean reduction of 6.8% on top of the climate change impacts. Groundwater flood hazard maps were developed and integrated with a social vulnerability index to identify 1.7 km2 of the Pang/Lambourn at high risk. In the Pang catchment this represents around 1400 properties. Climate and land use change scenarios suggest however that the risk of groundwater flooding in the catchment will decrease considerably (25-98%) over the next century. This reduction in risk is likely to make mitigation through targeted land use modification unnecessary.